题解 | #统计作答次数#

select
    count(1) as total_pv,
    count(submit_time) as complete_pv,
    count(distinct if(submit_time and score is not null,exam_id,null)) as complete_exam_cnt
from
    exam_record exam_record;
	第三个语句很关键，题目要求的是完成的试卷数，要避免作答了而没有交卷的情况